An ignition circuit of the above kind is disclosed, for example, in U.S. Pat. No. 4,979,477. A spark plug is connected to a voltage source via an electronic switch. The ignition switch is actuated by a control circuit which closes the switch per revolution of the crankshaft in dependence upon the crankshaft angle and additional operating parameters such as the rpm of the engine and triggers an ignition spark. If the rpm exceeds a pregiven limit rpm, the control circuit holds the switch open and suppresses the ignition spark over at least one crankshaft revolution. This leads to a drop in rpm so that the rpm cannot increase beyond a permissible maximum rpm.
The known ignition switch makes possible a precise limiting of rpm whereby damage because of excessive rpm can be reliably avoided. However, depending upon the displacement of the engine and the apparatus driven by the engine, ignition uniformities have been determined in practice whereby inherent oscillations or vibrations can be excited. These can lead to an increased vibration at the handles of the portable handheld work apparatus.